In the last year, 30 researchers have used the resources of the Laboratory of Cellular and Molecular Biology Microscopy Core. While most of the researchers come from the Laboratory of Cellular and Molecular Biology, the Core has been used by scientists from the Laboratory of Metabolism (Protein Section), the Laboratory of Cellular Oncology, the Cell and Cancer Biology Branch and the Laboratory of Experimental Carcinogenesis. Almost all of the Principal Investigators in the Laboratory of Cellular and Molecular Biology have projects that involve the Core facility. Dr. Lawrence Samelson uses Core resources for the project "Biochemical Basis of T Cell Activation". Researchers working with Dr. Carol Clayberger have used the facility for the projects "Regulation of RANTES Expression in T Lymphocytes" and "Function of Granulysin". The Core has been involved with two projects from Dr. Stanley Lipkowitz, "Identification of Molecular Targets in Triple Negative Breast Cancer" and "Cbl Proteins as Regulators of Tyrosine Kinase Signaling". Dr. Carole Parent's project, "Signaling Events Regulating Chemotaxis" uses all of the Core instruments. Dr. Paul Randazzo has made extensive use of the Core for the project "Regulation of ADP-ribosylation factor". The Core facility has assisted Dr.Jeffry Rubin with the project "Secreted Frizzled-Related Proteins and Wnt Signaling". Dr. Ying Zhang uses Core instruments for the project "Molecular Mechanisms of TGF-beta Signaling Pathway". In addition, the Core facility has been used by personnel working with Principal Investigators from other groups including work with Dr. Michael Bustin on the nucleosome binding protein HMGN1 and the role of heterochromatin formation in cell migration and a project of Dr. Gilbert Smith on channeling mouse ES cells into mammary epithelial precursors. In work done with Dr. Lawrence Samelson, the Core PI has been the lead investigator in the project, "The Cell Biology of the Calcium Release-Activated Calcium Channel in T Cells". While this project is presented in his annual report, a brief summary is also included here. We previously determined that fluorescently tagged versions of the calcium detector, STIM1, and the calcium channel subunit, Orai1, cluster in punctae near the contact surface upon T cell antigen receptor activation. We also observed the colocalization of these molecules at the opposite pole of the activated T cells in cap-like structures. We continue to study the function of these caps and are currently examining the effect of mutations in the STIM1 protein on cap formation. In addition, collaborative work with Dr. Janis Burkhardt showed that cap formation is distinct from the formation of the distal pole complex and that the requirements for ERM protein activity are different for formation of STIM1 caps and distal pole complexes. The Core has also acquired a microscope capable of Total Internal Reflection Fluorescence (TIRF) imaging. This high resolution instrument allows a resolution in the z dimension of less than 200 nm, below the diffraction limit. This system is currently being used to study the uptake of EGF for the project "Regulation of ADP-ribosylation factor" with Dr. Paul Randazzo.